344 W. B. CLARK— UPPER CRETACEOUS FORMATIONS OF NEW JERSEY. 



similar occur in the overlying Manasquan formation. The calcareous 

 beds, on the other hand, are unique, nothing similar being known in any 

 of the other Cretaceous formations. The persistency and great local 

 thickness reached by these beds render this deposit one of, if not the 

 most striking in the entire Cretaceous series of the northern Atlantic 

 Coastal plain. 



The Manasquan formation is typically composed of very pure green- 

 sands, which in their upper members particularly may become at times 

 ash-colored by an admixture of argillaceous elements. These ashy and 

 drab colored marls are thoroughly characteristic of the Manasquan forma- 

 tion, the more argillaceous members of the lower formations possessing 

 rather a chocolate than an ashy color. The pure greensands too are gen- 

 erally lighter green than the giauconitic deposits of earlier horizons, their 

 nearest allies being seen in the greensands of the Rancocas formation. 



The deposits of the Shark River formation are typically bluish colored 

 greensands which become at the top often indurated into stony bands. 

 They are more like the greensands of the Manasquan formation than of 

 any of the preceding formations, but nevertheless possess an individu- 

 ality of their own. 



GEOGRAPHICAL VARIATION IN THE MATERIALS. 



Very marked differences are recognized in the materials of the Upper 

 Cretaceous formations in the various parts of the northern Atlantic 

 Coastal plain. With some exceptions the formations are much more 

 fully developed in the north and gradually decline both in thickness and 

 in divisional distinctness toward the south. 



The Matawan formation, which has a thickness of fully 275 feet in 

 northern New Jerse} 7 , gradualry thins southward until it finally disappears 

 in southern Maryland. The divisions also, which are clearly denned 

 in the north, become gradually obscured in central New Jersey, and farther 

 south are not recognized, the materials becoming practically homogene- 

 ous throughout. The well marked clays and clearly defined sands of 

 the north gradually give place to micaceous sandy clays and maris that 

 show in a remarkable degree an admixture of the more characteristic 

 substances found in the New Jersey deposits. 



The Monmouth formation changes greatly in character between north- 

 ern New Jersey and central Maryland where it finally disappears. In 

 the north the three divisions previously described are clearly denned, 

 while throughout central and southern New Jersey the upper sandy 

 member is either wanting or replaced wholly or in part by fine argilla- 

 ceous deposits, the lower sandy member at the same time steadily increas- 

 ing from the north toward the south until it changes from an insignificant 



